The big picture: Fungi play a role in plant function
- 100,000 species described
- estimated 1.5 millions species
- diverse size, morphology and habitats
- Heterotrophic: eat via absorption
- parasites, decomposers, mutualists
- cycle nutrients via decomposition
- Cell walls made of chitin
- mushrooms are only a part of the body
- filaments belowground absorb things

All Fungi share traits related to nutrition
- Use enzymes to break down compounds
- diverse enzymes for diverse food sources
- Heterotrophs: absorb nutrients from environment
- decomposers: break down dead things
- parasites: absorb from host
- mutualist: absorb/share with host

Fungal body plan: Not-motile

Most hyphae divided into cells by septa


Mycelium: huge surface and volume for absorption


Specialized hypae in many types of fungi
- Specialized hyphae for feeding on live animals
- Specialized hyphae that allow them to extract nutrients from plants


Mycorrhizal fungi: sharing with plants
- ~80-90% of plants have association with fungus
- fungi grown in/around plant roots
- share resources
- one of the most widespread mutualisms
- 2 main types:
- Ecto- and Endo- mycorrhizae
- diverse array of species for each
- Association now key for plants to thrive
- fungi more efficient @ nutrient uptake


- Branching hyphae used to exchange nutrients with plant hosts
- Ectomycorrhizal fungi sheath cell walls
- Hartig net surrounds epidermal cells
- Endomycorrhizal fungi invade cell walls
- Arbuscules: highly branched hypae inside cells
- often called ‘arbuscular’ mycorrhizae

Nutrient Exchange: Sharing is caring

- Inorganic nutrients imported to plant
- Carbon imported to fungus
- sugars from photosynthesis
- Possibly active & passive transport
Soil Life: Plant Roots, Fungi & Microbes
- Free-living microbial communities in soils breakdown organic matter
- plants cannot uptake organic compounds
- fungi lost breakdown enzymes via evolution
- Microbial communities are carbon limited
- plants exude carbon (simple sugars) from root tips
- exudates increases microbial activity
- Fungi are great at uptake and transport
- decomposers of some things
- carbon limited

Timing matters: Land plant evolution & fungi
- Fungal phyla associated with MS diverged prior to the divergence of land plants
- Oldest fungal fossils appear ~900 mya
- First terrestrial fungus ~ 460 mya
- What was the land like for first plants?
- What were early plants like?
- Plant land colonization likely facilitated by interactions with symbiotic fungi
- fossil evidence shows similarity in timing
- needs of both groups still relevant

Early lineage plant experiments with fungi: byrophytes
Humphreys et al. 2010

Timing matters: Fossil forests and fungi
- Vascular plants evolved secondary growth (wood), with lots of lignin
- lignin is hard to break down
- About 100 million years of trees sinking into swamps and not decaying
- carboniferous period = coal deposits
- Specialized phyla of fungi evolved as wood decay specialist
- ~295 mya (aka ‘white rot’ fungus)
- lignin and cellulose
- What what the world look like today, without this key cog in the carbon cycle?

The current state of agriculture: Role of fungi
- Dramatic ↑ in crop productivity last century
- development of pesticides, fertilizers
- plant breeding and genetic technologies
- Now, crop yields have plateaued & fertilizer production unsustainable
- climate change
- over population
- nutrient depletion
- energy prices
- High levels of fertilizer reduces fungal-root association
- Big challenges to global food security


Role of mycorrhizae in agrosystems: Nutrients
- Crop species are breed to be hyper-productive
- fast growing with high yields
- Roots will rapidly deplete soil nutrients
- creates depletion zones around root
- Mycorrhizae extend the reach of roots
- widening the depletion zone
- Mycorrhizae access nutrients in forms plants cannot
- phosphorus from DNA or bound to minerals

Role of fungi in agrosystems: Stress, Disease
- Pesticides hinder plant’s natural immune response
- fungicides are toxic to mycorrhizal fungi
- Fungi colonizing roots physically exclude and protect from pathogens
- fungi release antibiotic substances
- Communication through fungi allows neighboring plants to know of pest attacks
- Mycorrhizal inoculation enhanced enzyme response to tomato blight infection

Sustainable agricultre with mycorrhizae

- Plant herbivory signals through fungal network between plants
- neighbors can turn on chemical defenses
- fungi help induce these chemical defenses (VOC’s)
- Nutrients benefits of symbiosis mean more flowers & nectar
- Fungal hypae release polysaccrides that bind soil particles
- holds more water
- stores more carbon
- reduces erosion & leaching
- improves microbial biodiversity
Should we also innoculate crops?
- Commercial fertilizers (NPK) are water-soluble
- short term availability
- requires heavy fertilizer application
- Natural abundances of soil nutrients exist, just not readily/easily accessible to plants
- Tilling soil reduces natural mycorrhizal associations
- Commercial inoculates add fungal spores, which are activated by root exudates

Are fungi always a good thing?
- Fungal pathogens exist (non-mycorrhizal)
- Not all crops have fungal symbioses
- broccoli, mustard, spinach, beets
- does this create competition?
- Dependency on mycorrhizae varies greatly
- How far does ‘sharing is caring’ go?
- can the relationship become parasitic?
